This invention relates in general to interfaces and junction boxes and in particular to multiple connected junction boxes that include logic functions.
Robotics is being increasingly being used in manufacturing situations to handle work pieces. Such robotic devices are known to pick up a work piece, transport the work piece to a work station, such as a numerically controlled machining operation, and install the work piece upon the work station. The robotic devices often include an arm that can swing, extend and elevate to move the work piece. The work piece itself is held in a gripper attached to the end of the arm. Such grippers are usually designed to accommodate the specific work piece and can include a plurality of fingers that close upon and thereby grasp the work piece.
The grippers are usually equipped with a plurality of position sensors that determine the position of the gripper fingers relative to the work piece. Such position sensors may be simple limit switches that are mechanically closed or opened upon contact with the work piece or may be more sophisticated proximity sensors that generate an output current or voltage as the fingers approach the work piece. Position sensors also can be mounted upon the robotic arm itself. The proximity type position sensors typically have an output stage that provides the sensor output signal to the robotic device. Upon receiving sensor output signals that all of the fingers are in place upon the work piece, the robotic device will proceed to the next step of its cycle, such as, for example, transporting the work piece to the next work station. Thus, the robotic device must receive a number of sensor output signals.
Position sensors also find wide spread use on machine tools and other mechanical devices where automatic control of movement is required. Thus, automatic processing machines and manufacturing equipment frequently include position sensors in their control systems to provide input signals to their logic circuits.
As described above, the position sensor output signals may be current sources generated by PNP output transistors or current sinks generated by NPN output transistors. Also, the input circuit of the associated robotic device may include either PNP or NPN devices. In the past, a specific junction box that is compatible with both the specific sensor output signal and the specific robotic device input signal requirements has been provided. This has increased the complexity of the design of robotic devices. Accordingly, it would be desirable to provide a common junction device or box that would be compatible with the different sensor output signals. It also would be desirable to provide a logic function in the junction device or box to provide a single output signal to the robotic device once all the sensors are indicating a closed status. By moving the logic to the junction box or device, the complexity of the robotic device wiring would be significantly reduced.
Additionally, it is known to connect several proximity sensors in series. Thus, an input signal is provided when all of the sensors are in a “closed position”. With a prior art junction box, the common signal generated by the series connected proximity sensors is passed directly to the junction box output. However, it has been observed that when more than two proximity sensors are connected in series, the cumulative voltage drop across the sensors degrades the output signal excessively. Accordingly, it would be desirable to provide a junction box or device that is not affected by the series connection of sensors on an input to the box. Additionally, it would be desirable to have an expandable capability to accommodate a variable number of sensors that are connected in series.